Engines may utilize a turbocharger or supercharger to compress ambient air entering the engine in order to increase power. Compression of the air may cause an increase in air temperature, thus, an intercooler or charge air cooler (CAC) may be utilized to cool the heated air thereby increasing its density and further increasing the potential power of the engine. Condensate may form in the CAC when the ambient air temperature decreases, or during humid or rainy weather conditions, where the intake air is cooled below the water dew point temperature. Further, when the charge air entering the CAC is boosted (e.g., an induction pressure and boost pressure are greater than atmospheric pressure), condensate may form if the CAC temperature falls below the dew point temperature. As a result, condensate may collect at the bottom of the CAC, or in the internal passages of the CAC. When torque is increased, such as during acceleration, increased mass air flow may strip the condensate from the CAC, drawing it into the engine and increasing the likelihood of engine misfire and combustion instability.
Other attempts to address condensate formation include restricting intake air travelling through the CAC or restricting ambient air flow to the CAC in order to increase the temperature of CAC air. One example approach is shown by Craig et al. in U.S. Pat. No. 6,408,831. Therein, the intake air temperature is controlled by an ambient air flow restriction system and an intake air flow restriction system. A controller defines the position of these restriction devices and is connected to a plurality of sensors which measure different variables such as ambient air and intake air temperatures.
However, the inventors herein have recognized potential issues with such systems. Specifically, blocking or restricting cold air from flowing through the CAC may be challenging and expensive to implement. Further, cooling airflow flowing toward the CAC may also be used to cool other engine system components. Thus, restricting cooling airflow to the CAC may also restrict cooling airflow to the other engine system components.
In one example, the issues described above may be addressed by a method for adjusting a secondary throttle positioned downstream of a compressor and upstream of a charge air cooler responsive to condensate forming conditions at the charge air cooler. For example, adjusting the secondary throttle may include decreasing an opening of the secondary throttle in response to a condensate level in the CAC increasing above a threshold level. Decreasing the opening of the secondary throttle may decrease the pressure, and subsequently the relative humidity, at the CAC. As a result of decreasing the CAC pressure, the condensate level within the CAC may decrease, thereby reducing the likelihood of unstable combustion and/or engine misfire due to condensate ingestion.
As one example, the secondary throttle is positioned within an intake passage of an engine, upstream of the primary throttle and CAC and downstream of a compressor. The primary throttle may be adjusted based on torque demand during engine operation when the condensate level is greater than the threshold level. Further, the secondary throttle may be fully open during this time. However, when the condensate level in the CAC increases above the threshold level, an engine controller may decrease the opening of the secondary throttle if the primary throttle is not fully open (as required by torque demand). The engine controller may also increase the opening of the primary throttle in order to compensate for decreasing the opening of the secondary throttle and continue to provide the demanded torque. The secondary throttle position may be reduced for a duration until the condensate level decreases and/or until torque demand increases requiring a larger opening of the secondary throttle. In this way, adjusting the positions of the primary throttle and the secondary throttle may reduce condensate accumulating within the CAC, thereby reducing the likelihood of condensate-related engine misfire events.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.